The invention relates to a process for controlling an internal combustion engine with a common rail injection system.
In a common rail injection system the rail pressure is regulated. The actual value of the rail pressure, thus the controlled variable, is gathered by an electronic controller by way of a rail pressure sensor. Said controller calculates the system deviation from a variance comparison of the rail pressure and determines by way of a rail pressure regulator a select signal for a setting element, for example, a suction throttle or a pressure regulating valve. Since the rail pressure represents a significant parameter for the injection quality, one must react to a defective rail pressure sensor with appropriate measures. The DE 199 16 100 A1 proposes in the case of a defective rail pressure sensor that one changes from normal operation to a start operation. In the start operation the rail pressure is controlled. In so doing, a high pressure pump is set to the maximum pump delivery rate; and a pressure regulating valve, which determines the outflow from the rail, is closed. The with this solution is the abrupt transition from the normal to the start operation, as well as the resulting high rail pressure.
The U.S. Pat. No. 5,937,826 discloses an emergency operation (limp home) for an internal combustion engine with a defective rail pressure sensor. In the emergency operation the high pressure pump is controlled by way of a characteristic diagram as a function of the engine speed and a desired rate of injection. The problem with this solution is that immediately after the transition into the emergency operation the rail pressure can increase due to the previous large system deviation. Thus, the engine speed can increase. This undefined operating state remains until the engine speed regulator reduces the desired rate of injection and controls the rail pressure indirectly by way of the characteristic diagram.
Therefore, the invention is based on the problem of making the transition from the normal operation to the emergency operation safer.
The problem is solved by a process for controlling an internal combustion engine during which a rail pressure is regulated in normal operation, and upon detection of a defective rail pressure sensor the normal operation is switched to an emergency operation the rail pressure is controlled in accordance with a transition function which smoothly and reliably transitions rail pressure control from the normal operation to the emergency operation. Related embodiments are discussed further, below.
The invention provides that the transition from the normal operation to the emergency operation is determined reliably by a transition function. In normal operation this transition function is determined beforehand from the characteristics of the system deviation of the rail pressure as a function of time. In addition, the system deviations in one measurement period or a specifiable number of system deviations can be considered. As one measure, at the end of the normal operation the transition function defines a negative system deviation for the rail pressure regulator in accordance with the measurement period, logged during the normal operation, or the number of system deviations. An alternative measure provides that a correcting volumetric flow of the controlled system is specified by means of the transition function. The correcting volumetric flow is calculated from the difference between two system deviations. Both measures offer the advantage that a defined, continuous transition from the normal operation to the emergency operation takes place. The result of the direct impact of the transition function on the rail pressure regulator or the controlled system is a short reaction period after the rail pressure sensor fails.
At the end of the transition function a switch is made to the characteristic diagram, known from the prior art. A flanking measure provides a loading characteristic diagram, with which the values of the characteristic diagram are additionally weighted. In addition, the characteristic diagram is corrected by limit lines, whereby the indirect determination of the rail pressure is aided by the engine speed regulator.